Ultra Rapid Fire, Mirror Mode

I think these game modes are one of the best game modes I have ever play, and probably the most loved game modes out there. Why doesn't Riot make these permanent game modes, or at least let the game mode be more frequent. I loved these game modes it sucks that these game modes aren't permanent. Ultra Rapid Fire, and Mirror Mode was by far my 2 favorites. If these game aren't permanent then can Riot make/change different game modes for each month, and whatever game mode is favored it comes up multiple times throughout the year. I don't know how the developing is and how hard it is to do this but Riot made it this far i'm sure they can take it 1 step further.